This Phase I SBIR application proposes the use of novel fluid-fluid waveguiding techniques as the basis of an on-chip flow cytometry technology. We have shown that refractive index-mismatched fluids may be used to create dynamic waveguides and that these guides may be used to quantify the concentration of particulates contained within the core fluid. We propose to demonstrate the feasibility and advantages of this technology by performing integrated on-chip activated platelet counts. This proposed application serves as a poignant illustration of this technology's potential as a point of care biomedical diagnostic tool. The specific aims of this proposal are to: 1) To configure flow conditions and optics for single cell detection sensitivity. We believe that the sensitivity limit of this technique will enable the detection and counting of individual cells or particles. 2) To combine this novel on-chip waveguiding technique with Metafluidics' existing expertise in microscale fluid and cell handling to perform a single-step whole blood assay. Success of this aim will be quantified through validation against standardized activated platelet counting protocols. Phase I success will set the stage for the maturation of this technology during Phase II, which will result in a piece of permanent hardware with which customized cartridges for virtually any assay may be used. This will produce a unique instrument that is broadly applicable as a focused diagnostic tool or a platform research aid.